What tests are recommended to assess atrioventricular conduction in a patient with classic Wenckebach and intermittent 3:2 AV block?

Electrophysiological Study (EPS) to Assess Conduction Site

In a patient with classic Wenckebach and intermittent 3:2 AV block, an electrophysiological study (EPS) with His bundle recording is the definitive test to determine the precise anatomical site of conduction block and assess risk for progression to higher-degree block. 1, 2

Why EPS is Critical in This Clinical Scenario

The surface ECG alone cannot reliably distinguish between AV nodal block (benign) and infra-Hisian block (high-risk) in Wenckebach patterns, particularly when:

• The QRS complex is wide or abnormal - suggesting possible infra-Hisian disease 2
• The shortest PR interval is excessively prolonged (≥0.3 seconds) - raising concern for His-Purkinje involvement 2
• Bundle branch block coexists with Wenckebach - indicating potential progression risk 2

What EPS Reveals Through His Bundle Recording

His bundle electrophysiology delineates three anatomical sites of AV block 1:

1. Proximal (supra-Hisian) - delay or block in the AV node
2. Intra-Hisian - delay or block within the His bundle itself
3. Infra-Hisian (distal) - block distal to the His bundle in the bundle branches

Surface ECG Correlations vs. EPS Precision

While surface ECG provides clues, it has significant limitations 1, 3:

• Type I second-degree AV block with narrow QRS - usually AV nodal, but may be intra-Hisian 1
• Type I second-degree AV block with wide QRS - may be in the AV node, within, or below the His bundle 1, 4
• Wenckebach with persistent right bundle branch block - 60-70% of cases have infra-Hisian block despite the Wenckebach pattern 4

Critical pitfall: Surface ECG Wenckebach patterns can be misleading. Progressive PR prolongation suggests AV nodal disease, but when QRS is wide, infra-Hisian conduction abnormalities are present in the majority of cases. 4

Class I Indications for EPS in Your Patient

The American Heart Association provides Class I recommendations for EPS 2:

• Athletes with Wenckebach AV block and coexisting bundle branch block - to identify intra-His-Purkinje or infra-His-Purkinje block that may require pacemaker therapy 2
• Any indication of risk for progression to higher-degree AV block - EPS determines site and duration of conduction delay 2

Prognostic Implications Based on Block Location

The anatomical site determined by EPS directly impacts management 3:

• AV nodal block - typically benign, rarely progresses, vagally mediated 3
• Infra-Hisian block - ominous prognosis, high risk of progression to complete heart block, often requires pacing even if asymptomatic 3, 4

Additional Diagnostic Tests to Consider

Before or alongside EPS 2:

• Exercise stress test - to assess if block improves with increased sympathetic tone (suggests AV nodal) or worsens (suggests infra-Hisian) 2
• 24-hour ambulatory ECG monitoring - if QRS is abnormal or shortest PR interval ≥0.3 seconds 2
• Echocardiogram - to exclude structural heart disease 2

The exercise stress test can sometimes distinguish 2:1 Wenckebach physiology at the AV node from true Mobitz type II block, but EPS may still be required in ambiguous cases. 2